a) Field of the Invention
The invention relates to a microscope with at least one beam splitter, particularly for examining fluorescing specimens.
b) Description of the Related Art
Reflector modules for fluorescence microscopy comprise two filters and a selectively acting splitter mirror.
The light exciting fluorescence in the specimen is made available through an excitation filter in a narrow band corresponding to the selected application method and in the required wavelength. The splitter mirror directs this light as efficiently as possible through an objective onto the specimen. The wavelength emitted at the latter, passes the splitter mirror again with an offset relative to the excitation light in the long-wave spectrum. This second passage through the splitter mirror must also be effected efficiently with respect to wavelength. A blocking filter arranged following the splitter mirror allows almost one hundred percent of the emitted light to pass, but possible components of the excitation light are held back just as completely.
FIG. 1 is a sectional view showing the illumination beam path BL traveling through the excitation filter AF for fluorescence excitation in a microscope, not shown, which is deflected at a beam splitter ST in the direction BL1 of an object via an objective, not shown.
The light OL coming back from the object travels via a blocking filter SF upward in the direction of an evaluating beam path with tube lens, not shown, and, for example, a TV camera.
A beam path RL, shown in dashed lines, shows an unwanted component of the illumination light BL which goes through the beam splitter ST and strikes the blackened rear wall R which is supposed to absorb this unwanted portion of the excitation light as completely as possible.
However, at this rear wall, a proportion RL1 is reflected and scattered at unavoidable miniature structures on the surface and travels at an angle back to the glass surface of the beam splitter ST and from the latter in the direction of observation/detection at an angle to the optical axis as unwanted reflected light RL2.
The angle-dependent blocking filter can also not completely filter out this component because of the angle to the optical axis.
As can be seen in FIG. 1, reflector modules constructed in the manner known heretofore bring about a partially indirect reflection or scattering of the excitation light which passes the splitter without reflection and travels back to the splitter and then into the emission channel. Since the beam angles are changed by this indirect reflection in such a way that they break the direction-dependent selectivity of the splitter and emission filter, the optical prerequisite for the background lighting is given. In the emission channel, like autofluorescence of glasses and coatings, it provides for lighting of the image background which reduces the intensity distance from the useful signal and accordingly makes detection of weak fluorescence signals difficult or impossible.